Enter Up, Up, Down, Down, Left, Right Left, Right, B, A, Start in the pause menu to upgrade your weapons fully.
Press Up, Up, Down, Down, Left, Right Left, Right, Y, B at the start screen of the original Contra game, then press start to begin the game with 30 lives.
At the title screen for Super C enter: Right, Left, Down, Up, B, and then Y
Complete the game on any difficulty to unlock Challenge Mode. This includes Easy.
Successfully complete the game under the Normal or Hard difficulty setting.
Successfully complete the game. Press Up(2), Down(2), or X(2) at the character selection screen to choose one of three alternate colors.
Lose a life precisely when you gain an extra life. You will now have 99 lives.